1. Field of the Invention
The present invention relates to a mobile terminal apparatus, and a control method and communication system for the apparatus, and more particularly, to a mobile terminal apparatus having the function of switching between communication systems intended for communication, and a control method and communication system for the apparatus.
2. Description of Related Art
Conventionally, as communication systems of cellular telephone apparatuses, for example, there have been various systems such as the W-CDMA system, GSM (Global System for Mobile Communications) system and the like, and systems have been considered that enable a cellular telephone apparatus to perform communication with some communication system to be usable in a communication area of a communication system using another communication system differing from the some communication system (see Patent Document 1). In this system, when a cellular telephone apparatus for performing communication with a communication system moves to a communication area of a communication system using some communication system differing from the communication system of the apparatus, the communication system is switched to the system adapted to the cellular telephone apparatus for the cellular telephone apparatus to communicate.
In this way, it is considered to be able to extend the available area of a cellular telephone apparatus for performing communication using only a single communication system.
Meanwhile, another method is also considered that communication systems are switched on the cellular telephone apparatus side corresponding to a communication system of a communication area (hereinafter, referred to as an existing area) where the cellular telephone apparatus exists. In this case, without a change on the communication system side that is a communication target of the cellular telephone apparatus, only by switching between communication systems on the cellular telephone apparatus side, it is possible to support various communication systems (communication systems) to perform communication.
However, in the method in which a cellular telephone apparatus switches between communication systems according to the existing area, the cellular telephone apparatus needs to detect a communicable communication system of the communication system in the existing area. In this case, the cellular telephone apparatus needs to periodically transmit and receive signals to monitor a communicable communication system in the existing area with a plurality of communication systems, and a problem arises that power consumption increases and becomes a cause of accelerating exhaustion of the battery, as compared with the case of periodically issuing signals to monitor the communication environment with a single communication system.